Revision as of 12:30, 20 November 2013

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PostgreSQL is an open source, community driven, standard compliant object-relational database system.

This document describes how to set up PostgreSQL. It also describes how to configure PostgreSQL to be accessible from a remote client. If you need help setting up the rest of a web stack, see the LAMP page and follow all of the sections except the one related to MySQL.

Before you start

Several sections have instructions stating "become the postgres user". Execute the following to get a shell as the postgres user:

su root
su - postgres

Otherwise sudo can be used:

sudo -i -u postgres

Installing PostgreSQL

Installpostgresql from the official repositories. Before PostgreSQL can function correctly, the postgres user needs to be given ownership of several files and directories, and the database cluster must be initialized. The following steps set sane defaults.

Start PostgreSQL and, optionally, add it to the list of daemons that start on system startup:

# systemctl start postgresql
# systemctl enable postgresql

Create your first database/user

Become the postgres user. Add a new database-user using the createuser command.

If you create a user as per your login user ($USER) it allows you to access the postgresql database shell without having to specify a user to login (which makes it quite convenient).

e.g. to create a superuser

$ createuser -s -U postgres --interactive

Enter name of role to add: myUsualArchLoginName

Create a new database over which the above user has read/write privileges using the createdb command.

From your login shell (not the postrgres user's):

$ createdb myDatabaseName

Familiarize with PostgreSQL

Access the database shell

Become the postgres user. Start the primary db shell, psql, where you can do all your creation of databases/tables, deletion, set permissions, and run raw SQL commands. Use the "-d" option to connect to the database you created (without specifying a database, psql will try to access a database that matches your username)

$ psql -d myDatabaseName

Some helpful commands:

Get help

=> \help

Connect to a particular database

=> \c <database>

List all users and their permission levels

=> \du

Shows summary information about all tables in the current database

=> \dt

exit/quit the psql shell

=> \q or CTRL+d

There are of course many more meta-commands, but these should help you get started.

Configure PostgreSQL to be accessible from remote hosts

The PostgreSQL database server configuration file is postgresql.conf. This file is located in the data directory of the server, typically /var/lib/postgres/data. This folder also houses the other main config files, including the pg_hba.conf.

Note: By default this folder will not even be browseable (or searchable) by a regular user, if you are wondering why find or locate is not finding the conf files, this is the reason.

As root user edit the file /var/lib/postgres/data/postgresql.conf.
In the connections and authentications section uncomment or edit the listen_addresses line to your needs:

listen_addresses = '*'

Take a careful look at the other lines.
Hereafter insert the following line in the host-based authentication file /var/lib/postgres/data/pg_hba.conf. This file controls which hosts are allowed to connect, so be careful.

# IPv4 local connections:
host all all your_desired_ip_address/32 trust

where your_desired_ip_address is the IP address of the client.
After this you should restart the daemon process for the changes to take effect with:

# systemctl restart postgresql

Note: Postgresql uses port 5432 by default for remote connections. So make sure this port is open and able to receive incoming connections.

For troubleshooting take a look in the server log file

tail /var/log/postgresql.log

Configure PostgreSQL to work with PHP

Install the PHP-PostgreSQL modules php-pgsql.
Edit the file /etc/php/php.ini. Find the line that starts with:

;extension=pgsql.so

Change it to:

extension=pgsql.so

If you need PDO, do the same thing with ;extension=pdo.so and ;extension=pdo_pgsql.so. If these lines are not present, add them. These lines may be in the "Dynamic Extensions" section of the file, or toward the very end of the file.
Restart the Apache web server:

# systemctl restart httpd

Change default data dir (optional)

The default directory where all your newly created databases will be stored is /var/lib/postgres/data. To change this, follow these steps:

Create the new directory and assign it to user postgres (you eventually have to become root):

Change default encoding of new databases to UTF-8 (optional)

Note: If you ran initdb with -E UTF8 these steps are not required

When creating a new database (e.g. with createdb blog) PostgreSQL actually copies a template database. There are two predefined templates: template0 is vanilla, while template1 is meant as an on-site template changeable by the administrator and is used by default. In order to change the encoding of new database, one of the options is to change on-site template1. To do this, log into PostgresSQL shell (psql) and execute the following:

First, we need to drop template1. Templates cannot be dropped, so we first modify it so it is an ordinary database:

cannot write to log file pg_upgrade_internal.log Failure, exitingMake sure you're in a directory that the "postgres" user has enough rights to write the log file to (/tmp for example). Or use "su - postgres" instead of "sudo -u postgres".

LC_COLLATE error that says that old and new values are differentFigure out what the old locale was, C or en_US.UTF-8 for example, and force it when calling initdb.

sudo -u postgres LC_ALL=C initdb -D /var/lib/postgres/data

There seems to be a postmaster servicing the old cluster.Please shutdown that postmaster and try again.Make sure postgres isn't running. If you still get the error then chances are these an old PID file you need to clear out.

ERROR: could not access file "$libdir/postgis-2.0": No such file or directory Retrieve postgis-2.0.so from postgis package for version postgresql 9.2 () and copy it to /opt/pgsql-9.2/lib (make sure the privileges are right)

Detailed instructions

Note that these instructions could cause data loss. Use at your own risk.

It is recommended to add the following to your /etc/pacman.conf file:

IgnorePkg = postgresql postgresql-libs

This will ensure you do not accidentally upgrade the database to an incompatible version. When an upgrade is available, pacman will notify you that it is skipping the upgrade because of the entry in pacman.conf. Minor version upgrades (e.g., 9.0.3 to 9.0.4) are safe to perform. However, if you do an accidental upgrade to a different major version (e.g., 9.0.X to 9.1.X), you might not be able to access any of your data. Always check the PostgreSQL home page (http://www.postgresql.org/) to be sure of what steps are required for each upgrade. For a bit about why this is the case see the versioning policy.

There are two main ways to upgrade your PostgreSQL database. Read the official documentation for details.

For those wishing to use pg_upgrade, a postgresql-old-upgrade package is available in the repositories that will always run one major version behind the real PostgreSQL package. This can be installed side by side with the new version of PostgreSQL. When you are ready to perform the upgrade, you can do

pacman -Syu postgresql postgresql-libs postgresql-old-upgrade

Note also that the data directory does not change from version to version, so before running pg_upgrade it is necessary to rename your existing data directory and migrate into a new directory. The new database must be initialized by starting the server, as described near the top of this page. The server then needs to be stopped before running pg_upgrade.

Troubleshooting

Improve performance of small transactions

If you are using PostgresSQL on a local machine for development and it seems slow, you could try turning synchronous_commit off in the configuration (/var/lib/postgres/data/postgresql.conf). Beware of the caveats, however.

synchronous_commit = off

Prevent disk writes when idle

PostgreSQL periodically updates its internal "statistics" file. By default, this file is stored on disk, which prevents disks spinning down on laptops and causes hard drive seek noise. It's simple and safe to relocate this file to a memory-only file system with the following configuration option: